654 GEOLOGICAL SURVEY OF IOWA. 



CRffiOIDEJ! AND OTHER ECHIIODERMATA OF THE WARSAW 



LIMESTONE. 



AT the present time, I am acquainted with four species of 

 PLATYCRINUS, one of ACTINOCRINUS, one of CYATHOCRINUS, one 



Of SCAPHIOCRINUS, two of DlCHOCRINUS, One Of FORBESIOCRINUS, 



and one of PENTREMITES, besides a species of ARCHJEOCIDARIS, 

 all undescribed and characteristic of this formation. It was 

 originally my intention to illustrate and describe these 

 species in this report ; but the subject has expanded before 

 me to such a degree that it has been necessary to curtail 

 the matter in hand, to avoid a too great extension of the 

 volume. 



The following species are characteristic of the horizon of 

 the Warsaw limestone. 



Dichocriims simplex. 



PLATE XXII. FIG. 12 a, b. 



Dichocrinus simplex : SHUMARD, Transactions Academy of Sciences of St. Louis, 1857, 



" CALYX beadshaped or cylindrico-elliptical, length and 

 breadth about equal ; plates rather thin and smooth (?}. Base 

 semiglobose, about two-thirds the entire height of the calyx : 

 the pieces of which it is composed are much thicker below 

 than above. The facet for articulating with the last joint of 

 the column is small, circular, and lies in a deep cavity which 

 is a little wider than the facet. Radial pieces higher than 

 wide, evenly convex and widest inferiorly : four of them 

 quadrangular, their inferior edges rounded ; one of them 

 pentagonal and wider : all the radial pieces differ from each 

 other in width. The anal piece resting on the base is all that 

 is known : it presents nearly the same form and dimensions 

 as the pentagonal radial piece. The column, arms, and vault 

 are unknown. 



" DIMENSIONS : Height of calyx, 4 lines ; diameter of the 



